The amygdala a walnut-sized structure in the brain is critical for processing a wider range of social and emotional stimuli than was previously suspected suggest two papers published online this week in Nature Neuroscience.

This area of the brain has long been associated with non-conscious processing of emotion; however, these studies show that this tiny area may also be involved in more sophisticated functions such as explicit social judgements and regulating personal space.

Patient SM, who has complete amygdala lesions, does not recognize fear when shown images of emotional faces, and based on human functional imaging and animal studies, it was thought that this was due to deficits in rapid processing of emotions. However, Naotsugu Tsuchiya and colleagues find that while SM does respond appropriately to fearful stimuli when under time pressure, she is profoundly impaired on categorizing emotional images of faces when given unlimited time. This suggests that the amygdala may be important for making conscious social judgements.

In a separate study, Kennedy and colleagues more closely examine their observation that SM lacks any sense of personal space. SM feels comfortable nearly nose to nose with the experimenters. She is aware that others prefer to stand further apart, but she simply doesn't feel the discomfort of close proximity. The authors also report that the amygdala is more active in control subjects when they are told that an experimenter is close by.

The results of these two studies indicate that the amygdala is critical for processing a wider range of social and emotional stimuli than previously suspected.